Aquarium filter



FIG. 1 is a perspective view of the aquarium filter showing our new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is an elevational view taken from one side thereof, the opposite side being a mirror image of the side shown;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a bottom plan view thereof; and

FIG. 6 is a top plan view thereof. 

The ornamental design for an aquarium filter, substantially as shown and described. 